This invention relates to infrared detectors comprising an envelope with a space in which a chemically-active getter is present, and further relates to methods of manufacturing infrared detectors.
U.S. Pat. No. 3,851,173 describes one example of an infrared detector comprising an envelope, a cold finger in the envelope and at least one detector element mounted on an end of the cold finger so as to be cooled by the cold finger in operation of the detector. The envelope has an outer wall extending around the cold finger and an infrared-transmissive window facing the detector-element end of the cold finger. A space is present between the cold finger and the window and outer wall of the envelope, and a chemically-active getter is present in said space to getter gases from the space.
In the form disclosed in U.S. Pat. No. 3,851,173 the envelope is a vacuum dewar having a vacuum space between inner and outer walls of the dewar envelope. The inner wall defines an inner chamber accommodating a cryogenic cooling element which serves to cool the inner wall end and hence the detector element thereon, during operation of the detector. The cooled inner wall forms the cold finger of the detector. A major cause of infrared detector failure is the gradual degeneration of the vacuum in the space between the inner and outer walls due to internal out-gassing of the various component parts of the detector exposed to the vacuum. In the detector of U.S. Pat. No. 3,851,173 a non-evaporable chemically-active SAES getter unit is mounted in the outer wall to maintain a good vacuum in the space between the outer wall and the cold finger. Such chemical getters are activated by being taken to a high temperature during or after evacuating and sealing the dewar envelope. This is normally achieved with an electrical heating element embedded in the getter material formed as a unit with electrical connection leads (not specifically shown in U.S. Pat. No. 3,851,173) passing through vacuum-tight seals in the dewar. U.S. Pat. No. 4,206,354 shows an example of such a dewar getter with its connection leads.